Insulated gate bipolar transistors (IGBTs) have been used in a variety of power, control, and electronic applications, such as, in motor controllers, in motor drives, and in appliance control. IGBTs are particularly suited for such applications because of their low on-state voltage drop and high switching speed.
Various structures for IGBTs, such as, planar IGBTs, trench IGBTs, and lateral IGBTs, have been designed to customize the operational properties of the device for particular applications. For example, planar or vertical IGBTs utilize a convenient structure for a high power (e.g., high voltage and high current) switch. The planar IGBT includes a collector at a bottom side, a gate at a top side, and an emitter surrounding the gate at the top side. Trench gate IGBTs have a similar general structure to the planar IGBTs. However, trench IGBTs include a trench within which the gate is situated. The trench reduces the on-state voltage drop of the device. The current path of planar and trench IGBTs is vertical from the collector to the emitter.
Lateral IGBTs are often employed in lower power control and detection circuits. Lateral IGBTs do not utilize the vertical structure of the planar and trench IGBTs, where collector and emitter contacts are provided on the top and on the bottom of the semiconductor material. Instead, lateral IGBTs generally include a substrate contact at a bottom side, a collector at one side of a top side, an emitter at the other side of the top side, and a gate disposed between the emitter and the collector at the top side. The current path of lateral IGBTs is horizontal (e.g., lateral) within the device from the collector to the emitter.
Generally, IGBTs, including planar IGBTs, trench IGBTs, and lateral IGBTs, are unidirectional in conducting current: only capable of conducting current in a single direction and only capable of blocking high voltage for punch-through structures in a single direction. Typically, power circuits, including conventional IGBTs, must include a diode coupled in anti-parallel with the collector and with the emitter of each IGBT because conventional (unidirectional) IGBTs cannot flow current in the opposite (reverse) direction. The diode conducts in the reverse direction with respect to the IGBT when a reverse bias voltage is applied against the collector and the emitter terminals, thereby providing a path for the current to flow from emitter to collector, a commutation feature needed in many power circuits. The requirement of a diode for each conventional IGBT increases the cost of circuits utilizing conventional IGBTs.
Additionally, power circuits, including conventional IGBTs, require two IGBTs coupled in anti-parallel to allow conduction in both directions. The requirement for the use of two conventional IGBTs to conduct in both directions increases the cost associated with power circuits.
Therefore, there is a need for an IGBT which can conduct current and block high voltage bidirectionally. Further, there is a need for power circuits which utilize bidirectional power switches. Further still, there is a need for a bidirectional high power lateral IGBT which can block over 1200V.